Photosensitive logic circuitry utilizing light pipe



Omer F. Hamann, La .l'olla, Calif., assigner to General u Dynamics Corporation, Rochester, N.Y., a corporation of Delaware u Filed Aug. 26, 1964. Ser. No. 392,260V 10 Claims. (Cl. Z50-227) out logic operations. Y

desirable to utilizeV AND gates and OR gates that have as 'i shunting effect of a large number of back: biased diodes .i connectedinparallel. In addition, isolation between input and output circuits connected to these gates is not complete.` J v .1- t f circuitry.

novel logic circuitry which provides complete isolation novel-logicscircuitr'y which may be embodied in virtually any desired`shapeso as to make maximum use of oddly shapedfuoolrs and crannies within a compact module.

provide a' mique digital-lto-analog converter.'

will become apparent from the following detailed descrip- `tion when considered in conjunction with the sole ligure.

is vprovided having a light source of a iirst frequency o r lightidetector positioned at theother end of the pipe.

vr. as ultraviolet light, are positioned alongthe length of the selectively energized and since they may he-noxrnally on pipe, digital-toanalog conversion may be accomplished.

one" in the output circuit only upont'oe application 1 of a fixed number of binary ones" in the input circuit, 1

" suchastwo,three, or more.

glass light pipes orhcould consist of an cpticalviiber cmcUirRY l y fi light pipe 2 may be broken along lines 4. The photo Thepresent invention relates to circuitry for carrying For certain applications in. the-.electronics field, itis Accordingly,'it is an object of thevpre'sent invention to f j z` provide novel logic circuitry which has a very large number of input terminals and which eliminates the problem f g oi sneak currents associated with conventional diode logic "f i' l t i 2b `l' htsourc 1. Thi tte uat'onis tected It isafurther object of the present invention to provide 15h ppc y lg e sa n -1 de between input andv output circuits coupled thereto.'

Itis a further object of the present invention to provide 35 It is a further object of the present invention to provide i novel logic circuitry having a very large number of inputf terminalsand which is relativelynexpensive tofabricate. ;It is yet a further obiectof the present invention to" Other objects and advantages of the presentinvention Inaccordancewith the present invention, 'a light pipev frequency band positionedat oneend of the pipe and a A plurality fof' generators of electromagnetic radiationV 1 having a'hi'gher frequency than said first frequency, such or normally oli', the circuitry may be utilized either as an, AND gate or an O R gate. Partial doping of photochrornic f j material results in' the carrying out of more complex logic- By partially attenuating light traveling throughout A'the Also, gates may beconstructed for producing a binary ln the preferred embodimentof the present invention disclosed in the ligure, a light source 1 is shown positioned 1 adjacent to one end of light pipe 2. Photcelectric detector; A3 is positioned at the other end of light pip: 2. Light pipe l '2 could consist of any of the widely available plastic or--f Patented Feb. 14, 1967.?

photochromic material, as is well known in the art, is a material that changes color or darkens as a result of the i absorption of short wavelength electromagnetic energy,

Y such as ultraviolet light or X-rays. The alkali halides 5. and silver halides exhibit this property. See page 158 i' of International Dictionary of Physics and Electronics,"-

Van Nostrand, 1956. In accordance with my invention,

chromic material would be diffused into areas 6. Afterthe completion of this dilusion, the pipe sections would again be joined at lines 4 by fusion. Tiny glass or plastic j chambers 7 are positioned adjacent pipe sections 6, as

shown, and contain a gas or vapor which emits a higher "frequency yelectromagnetic radiation (such as .ultraviolet light) .than the frequency of the electromagnetic radiation emittedby light source 1. The electrodes positioned with-A in-chambers 7 are coupled to a voltage'source 8 through switches 9. Each chamber 7 is, of course, connected to "7"? Yvoltage source 8 through an individual switch, only two of which are disclosed in the figure. When switch 9 isclosed, ionization of la gas, such as mercury vapor, con j tained within chamber 7 causes pipe section 6 to be exposed to this radiation. Thus, the gas chambers are bistable illuminating elements, since they are on when pulsed by an electric signal or oft when not pulsed. A color center is accordingly induced therein, which color center sharply attcnuates the light introduced into the by photoelectric detector 3. t f Let it be assumed that the disclosed circuitry is to be utilized as van OR gate.- Each switch 9 is open so that its -j' associated gas chamber does not'emit ultraviolet light. Accordingly. only binary zeros are applied to the input terminals of the'OR gate. As a result, no color centersl are induced within light pipe 2 and almost all of the light .introduced into light pipe 2 by `light source `1 emerges from the pipe and is detected by photoelectric detector .13.- Now let it be assumed that any one of the. switches 9 are closed thereby tomanifcst a one. vpotentialof voltage source 8 is impressedacross the electrodescontained'within a particular gas chamber 7 to cause ionization vof the gas contained thereinwhich, in` z tum", causes a darkening of -the section 6 adjacent to the .1 chamber.v This darkening sharply attenuates the lightj traveling through light pipe 2. which attenuation is d `'ftected by "photoelectric'detector 3, to signify ahiu'ary' "one." Where the disclosed circuitry .is utilized as an OR gate, halide doping is such that only one c olor center is v vnecessary to block out the light to produce a binary one! inthe .output circuit of photoelectric detector 3. 0b' viously the application of a voltage potential to more than fonev gas chamber-will not affect the situation, in the rnannerlof-a conventional OR-gate.- It should be noted that electrical isolation between the input circuits con-v taining switches 9 and the output circuit of photoelectn'c detector 3 is complete, unlike pnor art diode gates.' -i- 4Now let it be assumed that it is desired to operate the disclosed circuitry as an AND gate. All of the switches `9 associated with all of the gas chambers 7 are closed,j therebyto manifest binary "zeros in the input of the `AND gate in contrast tothe OR gate operation. Under these circumstances, the light introduced into light pipe 2 by light source 1 cannot reach photoelectrie detector v3 so that a binary zero is manifested in the output circuit of photoelectric detector 3. It' should be lapparent that this condition will continue as long'as one `or more of the switches 9 are closed. However, should 'each and every switch 9 become open to manifest binary onesf' the light from light source 1 will able to .a'ect photoelectric detector 3 so as to take advantage of every nooit and cranny available between electronic components 5 and 10. lf desired,

gas chamber 7 could be inserted directly within light pipe 2, but this would result in increased light attenu 1- ation at the boundaries of the gas and plastic or glass Further, light losses could media owing Vto reflection.

be ,induced if the end faces of the light pipes adjacent to the gas chambers were not perfectly parallel with one another.

pipe 2 with photochromic material, it is quite possible that the light pipe 2 may be .permeated throughout with the photochromic material during the initial light pipe manufacturing process. 1n this specification the word electromagnetic radiation having a frequency anywhere between 1011*' cycles per second up to 1021 -cycles per seov ond. All that is necessary is that a photochrornic ma- :l posed to higher frequency electromagnetic radiation.

the disclosed circuitry may be utilized as a digital-toanalog converter.

the light by eight units, light pipe sections 6' would at-l tenuate the light four units, whereas light pipe sections light from light source 1 would be attenuated by 12 units outputcircuit bf photoelectric detector 3. 1

Many other logic operations could l'ic'readilyv perhinaryfones are applied to the-inputs. g tj While there has been shown and described embodiment-ofthe invention, .other modifications will l readily occur to those skilled in the art. It is not, theref forepdesiredthat this invention be limited to the specific theappended claims to cover allmodications within vthe `spirit and scope of the invention.

" -iWhat is claimedis:

1. Logic circuitry comprising, photochromic substances at a plurality of locations along source positioned adjacent to one end of said light pipe `strength of the light generated by said light source and emerging from said pipe, means for causing said photo- 2. Logic circuitry compnsmg, alight pipe containing 1,. said pipe, said pipe having a lirst and second end, a light source positioned adjacent to one end of said light pipe to. cause a bnarytone z s to be manifested in the output circuit of the detector. f It should be noted that the light 'pipe may be shaped Instead of merely doping portions of light light 1s to be construed broadly and could include' lterial is provided within thelight pipe which atteuuatesf; lower frequency electromagnetic radiation upon being ert- I;

In addition to the logic functions set forth hereinabove,

For this application, the attenuation of light associated with any particular light pipe section;

' 6 would never completely blockthe light passing `through light'pipe 2. Instead, the degree of doping of sections 6 with photochromic material would be proportional to a-weighted binary code'to be converted to an analogff signal. For instance, light pipe sections 6 would attenuate 6 would attenuate the light two units, et cetera. Let it be assumed that a conventional binary code representing the number 12 is Ato be converted into its analog equivalentzColor centers would be induced insections 6 and 6' but not in sections 6" or 6"'. Accordingly,v the so that the complement of 12 would be manifested the f' i* formed. Partial doping could vresult in the complete at tenuationof light throughout the pipe only where two,4 `three, or more gas chambers are ionized. In other words, j the circuitry could produce a binary one only where a v minimum of two, three, or any other xed number of j arrangement shown and described, and it is intended in ai ugh: pipe morning wsaid pipe, said pipe having a first and second end,- a light-4 for inserting light into said pipe, means positioned adjacent to the other end of said pipe for detecting the-" chromic substances to at least partially absorb. said light generated by said light source thereby to change the intensity of the light detected `by; said photoelecte ie-Q :A

photochromic substances at a plurality of locations'along for inserting light into saidpipe, means positioned ad jacent to the other end of said pipe for detecting the emergence of the light generated by said light source from j; said pipe, means for causing said photochromic sub" i1-. "stances to at least partially absorb said light generated 1 by said light source thereby to change the intensity of the light detected by saidphotoelectric detector. 3. lLogic circuitry comprising, a light pipe containing photochromic substances at a plurality of locations along said pipe, said pipe having a first and second end, a light source positioned adjacent .to one end of said light pipe for inserting light into said pipe, means positioned ad jant to the other end of said pipe for detecting the strength of the light generated by said light source and f emerging from said pipe, means for Yexposing at least one section. of said pipe containing said photochromic' substances .to electromagnetic radiation having aA fre qocy higher than the frequency of said light generated I by id light source and for causing said photochromic substances to at least partially absorb said light generated by said light source thereby to change the intensity of the light detected by said photoelectric detector. f y 4. Logic circuitry comprising, a light 'pipe containing 5L-l f photochromic substances at a plurality of locations along said pipe, said pipe having a lxst and second end, a light source positionedadjacent' to one end of said light pipe for inserting light into said pipe, means positioned ad-: jacent to the other end of said pipe for detecting the '"f emergence of the light generated by said light source froiii l said pipe, means for exposing at least one section of said 30 pipe containing said photochromic substances to electro -magmetic radiation having a frequency higher than the 'frequency of said light generated by said light source and l* for causing said photocltroxnic substances to at least par- A tialiy absorb said- Iight generated by said light source 3 ther-:by to change the intensity of the light detected by said photoelectric detector. L.' 1

S. The invention as set forth in cla-im S'Wherein said 'meersior exposing includes one or more chambers ad' jacent said light pipe containing a gas which emits said 4g eleszromagnetic radiation having a frequency higher than the frequency o f said light generated by said light sourceu upon being ionized and means for selectively ionizing said f 6. The invention as set forth in claim 4 wherein said 'Ineens for exposing includes one or more chambers ad' ,-jarznt said light pipe containing a gas which emitssaid s-elearomagnetic radiation having a frequency higher than thefrequency of said light generated by said light sourcebeing ionized and means for selectively ionizing ,sd chambersig. 1 1.-'L'ogic circuitry comprising (FJ-fa light'pipe, v v' (b) means for deriving a b i-valued output in response to relative presence and "relative absence-of radiant venergy transmitted along said pipc, f (c) a plurality of signal input means optically coupled to said pipe at di'ercnt positions therealong, said input means each comprising 1 (i) a photochromic interface along seid pipe., (ii) signal responsive bistable illuminating ele- A. ments optically coupled to said interface, and (d)'means for applying binary input signals to said elements for conditioning them selectively into different one of their 'illuminating states.

The invention as set forth in claim 7 wherein said s. deriving means includes a photoresponsive element which can also produce an analog output signal, wherein each of said interfaces corresponds to a rdili'erent digit of a 70 digftal code, and wherein eachof said interfaces has the characteristic of presenting-a value of optical attenuation to radiant energy proportional tothe value of its corfresponding digit.. 1 n i .-9. I'he invention as set forth in claim 7 wherein said 75 dstivingmeans `.includes a source of said radiant energy at one end of said light pipe and a photoelectric detector l at the oppcsite end thereof, and' wherein said signal repsponsive bistable illuminating elemems include gas ds `cbargelamps.1 10. The invention as set forth in claim 9 wherein said input signal applying means includes electrodes in said lamps and means for applying operating voltages to said '4 y electrodes for normally biasingnsad lamps in selected` t f ones of said b-stable states. 4 I

WALTER STOLWEIN, Examiner.

l References Cited by the Examine:

. UNITED STATES PATENTS -f3,o85,469' 4/1963 Carlson 25m-229x -5 3,134,019 s/1964 Bishay 11s-106 X 3,169,190 2/1965 Ress 25o-227 x 6/1965 Binks 250--227 X RALPH G. NILSON, Primary Examiner. 

3. LOGIC CIRCUITRY COMPRISING, A LIGHT PIPE CONTAINING PHOTOCHROMIC SUBSTANCES AT A PLURALITY OF LOCATIONS ALONG SAID PIPE, SAID PIPE HAVING A FIRST AND SECOND END, A LIGHT SOURCE POSITIONED ADJACENT TO ONE END OF SAID LIGHT PIPE FOR INSERTING LIGHT INTO SAID PIPE, MEANS POSITIONED ADJACENT TO THE OTHER END OF SAID PIPE FOR DETECTING THE STRENGTH OF THE LIGHT GENERATED BY SAID LIGHT SOURCE AND EMERGING FROM SAID PIPE, MEANS FOR EXPOSING AT LEAST ONE SECTION OF SAID PIPE CONTAINING SAID PHOTOCHROMIC SUBSTANCES TO ELECTROMAGNETIC RADIATION HAVING A FREQUENCY HIGHER THAN THE FREQUENCY OF SAID LIGHT GENERATED BY SAID LIGHT SOURCE AND FOR CAUSING SAID PHOTOCHROMIC SUBSTANCES TO AT LEAST PARTIALLY ABSORB SAID LIGHT GENERATED BY SAID LIGHT SOURCE THEREBY TO CHANGE THE INTENSITY OF THE LIGHT DETECTED BY SAID PHOTOELECTRIC DETECTOR. 